问题 计算题

(10分)某石灰厂需要测定石灰石样品中CaC03的质量分数.小刚设计了下图所示装置来完成实验(杂质不与酸反应):

(1)写出下列仪器的名称①_______. 

(2)c装置应当选择I、Ⅱ中的_______ (填“I”或“Ⅱ”),其作用是______________.

(3)小华提出,要使测定结果更准确,应把A装置改成右图所示装置,并在反应前、后通入空气,其目的是_____________________.

(4)取用4g石灰石样品,把20g稀盐酸分四次加入石灰石样品中(样品中除碳酸钙外,其余物质既不与酸反应,也不溶于水),充分反应后经过过滤、干燥等操作,最后称量,最终实验数据如下表:

稀盐酸的用量第一次加入5g第二次加入5g第三次加入5g第四次加入5g
剩余固体的质量3211
求①该石灰石样品中碳酸钙的质量分数;

②该盐酸中溶质的质量分数.

答案

(1)锥形瓶      (2)I 充分吸收生成的CO2

(3)排除空气中CO2的干扰;使生成的CO2能被充分吸收

(4)①:75℅    ②:14.6℅

题目分析:(1)仪器的名称①锥形瓶. 

(2)c装置应当选择I、Ⅱ中的I,其作用是充分吸收生成的CO2

(3)小华提出,要使测定结果更准确,应把A装置改成右图所示装置,并在反应前、后通入空气,其目的是排除空气中CO2的干扰,使生成的CO2能被充分吸收.

(4)由题中数据可知:每次加入5g稀盐酸,将反应掉1g碳酸钙,但第四次加入盐酸后,剩余固体仍为1g,即杂质是1g。故:

①该石灰石样品中碳酸钙的质量分数为=75%;

②设该盐酸中溶质的质量分数为x%.

CaC03+2HCl=++CaCl2+H2O+CO2

100   73

1g    5g×x%

100:73=1g:5g×x%

x%=14.6℅。

答:该盐酸中溶质的质量分数为14.6℅。

点评:本题的难点在于根据题中数据分析盐酸与碳酸钙的数量关系,在根据化学方程式计算时,要注意解题的步骤,即设、写、找、列、解、答。

单项选择题
单项选择题

Like every dog, every disease now seems to have its day. World Tuberculosis (infections disease in which growths appear on the lungs) Day is on Saturday March 24th.

Tuberculosis was once terribly fashionable. Dying of "consumption" seems to have been a favorite activity of garret-dwelling 19th-century artists, h has, however, been neglected of late. Researchers in the field never tire of pointing out that TB kills a lot of people. According to figures released earlier this week by the World Health Organization, 1.6 million people died of the disease in 2005, compared with about 3m for AIDS and l m for malaria. But it receives only a fraction of the research budget devoted to AIDS. America’s National Institutes of Health, for example, spends 20 times as much on AIDS as on TB. Nevertheless, everyone seems to getting in on the TB-day act this year.

The Global Fund an international organization responsible fur fighting all three diseases but best known for its work on AIDS, has used the occasion to trumpet its tuberculosis projects. The fund claims that its anti-TB activities since it opened for business in 2002 have saved the lives of over 1m people. The World Health Organization has issued a report that contains some good news. Although the number of TB cases is still rising, the rate of illness seems to have stabilized; the caseload, in other words, is growing only because the population itself is going up.

Even drug companies are involved. In the nm-up to the day itself, Eli Lilly announced a $ 50m boost to its MDRTB Global Partnership. MDR stands for multi-drug resistance, and it is one of the reasons why TB is back in the limelight. Careless treatment has caused drug-resistant strains to evolve all over the world. The course of drugs needed to clear the disease completely takes six mouths, anti persuading people lo stay that course once their symptoms have gone is hard. Unfortunately, those infected with MDR have to be treated with less effective, more poisonous and more costly drugs. Naturally, these provoke still more. non-compliance and thus still more evolution.

The other reason TB is back is its relationship to AIDS. The (global Fund’s joint responsibility for the diseases is no coincidence. AIDS does not kill directly. Rather, HIV, the virus that causes it, weakens the body’s immune system and exposes the sufferer to secondary infections. Of these, TB is one of the most serious. It kills 200 000 AIDS patients a year. However, some anti-TB drugs interfere with the effect of some anti-HIV drugs. Conversely, in about 20% of cases where a patient has both diseases, anti-HIV drugs make the tuberculosis worse. The upshot is that 125 years after human beings worked out what caused TB, it is still a serious threat.

Which of the following proverbs is closest in meaning to the message the text tries to convey()

A. Forgive and forget

B. Forgotten, but not gone

C. When the wound is healed, the pain is forgotten

D. Every dog is valiant at his own door